Toward Defining Objective Criteria for Assessing the Adequacy of Assumed Axisymmetry and Steadiness of Flows in Rotating Cavities

2005 ◽  
Vol 128 (4) ◽  
pp. 708-716 ◽  
Author(s):  
G. D. Snowsill ◽  
C. Young
Keyword(s):  
Boundary Conditions ◽  
A Priori ◽  
Three Dimensional ◽  
Cyclic Symmetry ◽  
Acceptable Solution ◽  
Inappropriate Use ◽  
Flow Features ◽  
Computational Fluid Dynamics Cfd ◽  
Aero Engines ◽  
Multiple Reference

The need to make a priori decisions about the level of approximation that can be accepted—and subsequently justified—in flows of industrial complexity is a perennial problem for computational fluid dynamics (CFD) analysts. This problem is particularly acute in the simulation of rotating cavity flows, where the stiffness of the equation set results in protracted convergence times, making any simplification extremely attractive. For example, it is common practice, in applications where the geometry and boundary conditions are axisymmetric, to assume that the flow solution will also be axisymmetric. It is known, however, that inappropriate imposition of this assumption can lead to significant errors. Similarly, where the geometry or boundary conditions exhibit cyclic symmetry, it is quite common for analysts to constrain the solutions to satisfy this symmetry through boundary condition definition. Examples of inappropriate use of these approximating assumptions are frequently encountered in rotating machinery applications, such as the ventilation of rotating cavities within aero-engines. Objective criteria are required to provide guidance regarding the level of approximation that is appropriate in such applications. In the present work, a study has been carried out into: (i) The extent to which local three-dimensional features influence solutions in a generally two-dimensional (2D) problem. Criteria are proposed to aid in decisions about when a 2D axisymmetric model is likely to deliver an acceptable solution; (ii) the influence of flow features which may have a cyclic symmetry that differs from the bounding geometry or imposed boundary conditions (or indeed have no cyclic symmetry); and (iii) the influence of unsteady flow features and the extent to which their effects can be represented by mixing plane or multiple reference frame approximations.

Towards Defining Objective Criteria for Assessing the Adequacy of Assumed Axisymmetry and Steadiness of Flows in Rotating Cavities

2005 ◽  
Author(s):  
G. D. Snowsill ◽  
C. Young
Keyword(s):  
Boundary Conditions ◽  
A Priori ◽  
Cavity Flows ◽  
Cyclic Symmetry ◽  
Acceptable Solution ◽  
Inappropriate Use ◽  
Rotating Cavity ◽  
Flow Features ◽  
Aero Engines ◽  
Multiple Reference

The need to make a priori decisions about the level of approximation that can be accepted — and subsequently justified — in flows of industrial complexity is a perennial problem for CFD analysts. This problem is particularly acute in the simulation of rotating cavity flows, where the stiffness of the equation set results in protracted convergence times, making any simplification extremely attractive. For example, it is common practice, in applications where the geometry and boundary conditions are axisymmetric, to assume that the flow solution will also be axisymmetric. It is known, however, that inappropriate imposition of this assumption can lead to significant errors. Similarly, where the geometry or boundary conditions exhibit cyclic symmetry, it is quite common for analysts to constrain the solutions to satisfy this symmetry through boundary condition definition. Examples of inappropriate use of these approximating assumptions are frequently encountered in rotating machinery applications — such as the ventilation of rotating cavities within aero-engines. Objective criteria are required to provide guidance regarding the level of approximation that is appropriate in such applications. In the present work, a study has been carried out into: • The extent to which local 3-D features influence solutions in a generally 2-D problem. Criteria are proposed to aid in decisions about when a 2-D axisymmetric model is likely to deliver an acceptable solution. • The influence of flow features which may have a cyclic symmetry that differs from the bounding geometry or imposed boundary conditions (or indeed have no cyclic symmetry). • The influence of unsteady flow features and the extent to which their effects can be represented by mixing plane or multiple reference frame approximations.

Assessment of Unsteady Flows in Turbines

1992 ◽  
Vol 114 (1) ◽  
pp. 79-90 ◽  
Author(s):  
O. P. Sharma ◽  
G. F. Pickett ◽  
R. H. Ni
Keyword(s):  
Unsteady Flow ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Experimental Investigations ◽  
Flow Parameters ◽  
Research Activities ◽  
Flow Features ◽  
Computational Fluid Dynamics Cfd ◽  
Turbine Design ◽  
The Impact

The impacts of unsteady flow research activities on flow simulation methods used in the turbine design process are assessed. Results from experimental investigations that identify the impact of periodic unsteadiness on the time-averaged flows in turbines and results from numerical simulations obtained by using three-dimensional unsteady Computational Fluid Dynamics (CFD) codes indicate that some of the unsteady flow features can be fairly accurately predicted. Flow parameters that can be modeled with existing steady CFD codes are distinguished from those that require unsteady codes.

Numerical Simulation of the Laminar Flow Field in Stirred Tank with Double Layer Combined Impeller Stirring Eccentrically

2015 ◽  
Vol 779 ◽  
pp. 125-132
Author(s):  
Ying Na Liang
Keyword(s):  
Flow Field ◽  
Double Layer ◽  
Three Dimensional ◽  
Stirred Tank ◽  
Flow Structures ◽  
Practical Application ◽  
Three Dimensional Flow ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method ◽  
Multiple Reference

Computational fluid dynamics (CFD) method was applied to study the flow field in cylindrical stirred tank mixing non-Newtonian fluid with double layer combined impeller of upper-straight-blade and lower-inclined-blade. The laminar model and the multiple reference frame (MRF) were employed to simulate the three-dimensional flow field in stirred tank with double layer combined impeller rotating at a constant speed of 200 r/min mixing the mixture of glycerin and water centrally、eccentrically and relative eccentrically, and three different flow structures in stirred tank were obtained. Analyzing the velocity vectors, the velocity contours and the axial、radial and tangent velocity distribution curves, the rule of velocity field with the blade combined form and the stirring structure was discussed. The research provided the valuable reference for the design and practical application of the laminar stirred tank.

Numerical Study of the Winter-Kennedy Method—A Sensitivity Analysis

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Binaya Baidar ◽  
Jonathan Nicolle ◽  
Chirag Trivedi ◽  
Michel J. Cervantes
Keyword(s):  
Boundary Conditions ◽  
Secondary Flow ◽  
Numerical Study ◽  
Flow Behavior ◽  
Three Dimensional ◽  
Flow Distribution ◽  
Local Flow ◽  
Spiral Case ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Changes

The Winter-Kennedy (WK) method is commonly used in relative discharge measurement and to quantify efficiency step-up in hydropower refurbishment projects. The method utilizes the differential pressure between two taps located at a radial section of a spiral case, which is related to the discharge with the help of a coefficient and an exponent. Nearly a century old and widely used, the method has shown some discrepancies when the same coefficient is used after a plant upgrade. The reasons are often attributed to local flow changes. To study the change in flow behavior and its impact on the coefficient, a numerical model of a semi-spiral case (SC) has been developed and the numerical results are compared with experimental results. The simulations of the SC have been performed with different inlet boundary conditions. Comparison between an analytical formulation with the computational fluid dynamics (CFD) results shows that the flow inside an SC is highly three-dimensional (3D). The magnitude of the secondary flow is a function of the inlet boundary conditions. The secondary flow affects the vortex flow distribution and hence the coefficients. For the SC considered in this study, the most stable WK configurations are located toward the bottom from θ=30deg to 45deg after the curve of the SC begins, and on the top between two stay vanes.

Three-Dimensional CFD Analysis of a Spring-Loaded Pressure Safety Valve From Opening to Re-Closure

2010 ◽  
Author(s):  
Xue Guan Song ◽  
Lei Cui ◽  
Young Chul Park
Keyword(s):  
Safety Valve ◽  
Three Dimensional ◽  
Cfd Model ◽  
Flow Features ◽  
Valve Opening ◽  
Computational Fluid Dynamics Cfd ◽  
Multiple Domains ◽  
Future Work ◽  
Mesh Technique ◽  
Detailed Picture

We describe the dynamic analysis of a spring-loaded pressure safety valve (PSV) using a moving mesh technique and transient analysis in computational fluid dynamics (CFD). Multiple domains containing pure structural meshes are generated to ensure that the correlative mesh could change properly without negative volumes. With a geometrically accurate CFD model including the PSV and vessel rather than only the PSV, the entire process from valve opening to valve re-closure is presented. A detailed picture of the compressible fluid flowing through the PSV is obtained, including flow features in the very small seat region. In addition, the forces on the disc and its motion are monitored. Results from the model were very useful in investigating the dynamic and fluid characteristics of the PSV. Our practical CFD model has the potential to reduce the costs and risks associated with the development of new pressure safety valve designs. Future work will focus on improving the spring stiffness and seat region to eliminate or reduce vibration during the re-closure process.

FSI Methodology for Analyzing VIV on Subsea Piping Components With Practical Boundary Conditions

2013 ◽  
Author(s):  
Marcus Gamino ◽  
Samuel Abankwa ◽  
Raresh Pascali
Keyword(s):  
Boundary Conditions ◽  
Three Dimensional ◽  
Cost Effective ◽  
General Assumption ◽  
Computational Simulations ◽  
Element Analysis ◽  
Structure Interaction ◽  
The Finite Element Analysis ◽  
Computational Fluid Dynamics Cfd ◽  
Computational Methodology

A general assumption in performing vortex-induced vibration (VIV) analysis of pipeline free spans is both ends of the free span are fixed and/or pinned in order to simplify computational simulations; however, DNV Recommended Practice F105 states that these boundary conditions must adequately represent the pipe-soil interaction and the continuality of the pipeline. A computational methodology is developed to determine the effects of pip-soil interaction at the ends of a free span. Three-dimensional fluid-structure interaction (FSI) simulations are performed by coupling the computational fluid dynamics (CFD) codes from STAR-CCM+ with the finite element analysis (FEA) codes from ABAQUS. These FSI simulations in combination with separate coupled Eulerian-Lagrangian (CEL) simulations are modeled to mimic real word conditions by setting up boundary conditions to factor in the effects of pipe-soil interaction at the ends of the span. These simulations show a mitigation of overall stresses to the free spans; as a result, the integration of pipe-soil interaction in free span assessment may prove cost effective in the prevention of unnecessary corrective action.

A Simple Computer Program to Model Three-Dimensional Underground Heat Flow With Realistic Boundary Conditions

1983 ◽  
Vol 105 (1) ◽  
pp. 42-49 ◽  
Author(s):  
P. D. Metz
Keyword(s):  
Heat Flow ◽  
Boundary Conditions ◽  
Computer Program ◽  
Three Dimensional ◽  
Companion Paper ◽  
Coupled Systems ◽  
Moisture Movement ◽  
Solar Heat ◽  
Flow Equations ◽  
Flow Features

A FORTRAN computer program called GROCS (Ground Coupled Systems) has been developed to study three-dimensional underground heat flow. Features include the use of up to 30 finite elements or “blocks” of earth which interact via finite difference heat flow equations and a subprogram which sets realistic time and depth-dependent boundary conditions. No explicit consideration of moisture movement or freezing is given. GROCS has been used to model the thermal behavior of buried solar heat storage tanks (with and without insulation) and serpentine pipe fields for solar heat pump space conditioning systems. The program is available independently or in a form compatible with specially written TRNSYS component TYPE subroutines. This paper first describes the approach taken in the design of GROCS, the mathematics contained and the program architecture. Then, the operation of the stand-alone version is explained. Finally, the validity of GROCS is discussed. A companion paper serves as a user’s guide to the TRNSYS-compatible subroutine version.

Thermodynamically Admissible Motion Past Rigid Obstacles With Isentropic or Nonisentropic Fluid–Solid Interfaces

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Gerald G. Kleinstein
Keyword(s):  
Boundary Conditions ◽  
Stokes Equations ◽  
A Priori ◽  
Three Dimensional ◽  
Jump Condition ◽  
Navier Stokes ◽  
Heat Conducting ◽  
Material Interfaces ◽  
Material Interface ◽  
Solid Interface

The motion of a fluid in a defined domain is called thermodynamically admissible if it satisfies the global system of the principles of balance of continuum mechanics and the principle of entropy or its equivalent differential system, consisting of differential equations and jump conditions. In an earlier publication, we have shown that the motion of a three-dimensional rigid body in an irrotational viscous and heat-conducting fluid violates the entropy jump condition, referred to as the Clausius–Duhem jump condition. Such a motion is thermodynamically inadmissible and could not persist. In a more recent publication, we have demonstrated that if the fluid–solid interface is isentropic, boundary conditions at a material interface, such as the no-slip condition and the continuity of the temperature, follow directly from the Clausius–Duhem jump condition. It is the purpose of this analysis to extend this methodology for the derivation of boundary conditions at isentropic material interfaces to nonisentropic material interfaces. We show that if the boundary conditions at the fluid–solid interface are a priori selected to satisfy the Clausius–Duhem jump condition, the resulting motion as described by the solution of the Navier–Stokes equations—whether the interface is isentropic or nonisentropic—is thermodynamically admissible.

Calculation of Intake-Fan-Bypass Interaction With a Fan Similarity Model

2018 ◽  
Author(s):  
Mauro Carnevale ◽  
Feng Wang ◽  
Luca di Mare
Keyword(s):  
Boundary Conditions ◽  
Three Dimensional ◽  
Coupled System ◽  
Design Stage ◽  
Modern Trend ◽  
Test Case ◽  
Operation Condition ◽  
Present Contribution ◽  
Aero Engines ◽  
Very High

Modern trend in installation design is moving towards very high-bypass ratio turbofans. Very high-bypass turbofans represent an effective way of improving the propulsive efficiency of civil aero-engines. Such engines require larger and heavier nacelles, which partially offset the gains in specific fuel consumption. The penalty associated with a larger installation can be mitigated by adopting thinner walls for the nacelle and by shortening the intake section. Such inlet sections are characterized by more restrictive operation condition because they are more prone to separation at high incidence flight conditions. Moreover, in short nacelle installations the by-pass guide vanes and pylon are closer to the fan blades and consequently the distortion due to potential effects induced by the presence of the pylon and non-axisymmetric OGV stage play a significant role in terms of unsteady interaction in the entire system. It is mandatory to consider the inlet, fan, bypass and pylon as a unique coupled system also at the design stage, for assessment of fan force. This kind of assessment is usually carried on by expensive URANS calculation. The factors leading to high computational demands are the spatial resolution required in the fan domain and the time resolution required to sample the fan blade passing frequency. Large savings are therefore possible if simplifications are introduced which relax the resolution requirements in the fan passages and change the nature of the computation into a steady-state computation for the ducts. The present contribution documents a simplified fan model for fan-intake computations based on the solution of the double linearization problem for unsteady, transonic flow past a cascade of thin aerofoils with finite mean load. The coupling with the intake flow and the bypass is performed by using the flow patterns at fan face and fan exit as boundary conditions for the fan model and computing circumferentially non-uniform boundary conditions for the intake and the bypass from the fan model. The computation of the flow in the intake, bypass and pylon is therefore reduced to a steady problem, whereas the computation of the flow in the fan is reduced to one steady problem and a set of linearised models in the frequency domain. The model is applied to a well-documented test case and compares favourably with experimental data and much more expensive three-dimensional, time domain computations.

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